Antibodies can exert anti-tumor effects via their ADCC (antibody-dependent cell-mediated cytotoxicity) activity or CDC (complement dependent cytotoxicity) activity. Antibodies are sugar chain-bound glycoproteins. It is known that an antibody's cytotoxic activity can vary depending on the types and amounts of sugar chains that bind to the antibody. In particular, it has been reported that the amount of fucose binding to an antibody is strongly involved in the cytotoxic activity (Shields et al., J Biol Chem., 277(30), 26733-26740, 2002). Furthermore, a method for producing a recombinant antibody not having fucose has been reported. Such method involves preventing an enzyme that catalyzes the binding of fucose to a sugar chain from being expressed upon antibody production in order to obtain an antibody with enhanced cytotoxic activity (International Patent Publication No. WO00/61739).